The present invention relates to a gear and rolling dies for forming a gear.
Generally, wiper motors include a drive shaft that has a worm gear molded onto one end of the drive shaft. One example of a wiper motor includes a metal drive shaft, and a resin worm gear (corresponding to a gearwheel) that is molded onto one end of the metal drive shaft. It is important that the worm gear (or gearwheel) be fixed to the drive shaft so as not to come off and not to rotate with respect to the drive shaft. Conventionally, a serration groove having concavities and convexities repeated circumferentially, and a concave groove-like slit having a ring shape engraved in the circumferential direction at an intermediate portion in the axial direction, have been provided on an outer peripheral surface of the worm gear in order to prevent the worm gear from coming off and rotating with respect to the drive shaft (refer to, for example, Japanese Published Examined Patent Application No. S63-53406).